Method of producing hydrocarbons from an oil shale formation

ABSTRACT

A method of producing hydrocarbons and optionally water-soluble minerals from a subterranean oil shale formation containing zone(s) of water-soluble minerals, by penetrating said formation with at least one borehole and leaching or dissolving the watersoluble minerals from the formation with a solvent fluid so as to form a cavern(s) and/or interconnected cavities, followed by fracturization and/or rubblization of the oil shale surrounding the caverns or cavities, and thereafter injecting into fracturized and/or rubblized zones, a pyrolyzing fluid to effect in-situ hydrocarbon recovery therefrom.

United States Patent Beard 4 1 Sept. 18,1973

[75] lnventor: Thomas N. Beard, Denver, C010.

[73] Assignee: Shell Oil Company, New York, N.Y.

[22] Filed: Sept. 24, 1970 [21] Appl. No.: 75,009

Related U.S. Application Data [63] Contindatft m-in-part of Ser. Fl(1677096 1, Oct. 28,

1968, abandoned.

[52] U.S. Cl. 299/4, 166/271 [51] Int. Cl E211) 43/28 [58] Field ofSearch 166/271, 272, 259, 166/261; 299/4, 5

[56] References Cited 3 UNITED STATES PATENTS 3,481,398 12/1969 Prats166/251 3,502,372 3/1970 Prats. 3,393,013 7/1968 Hammer 3,018,095

1 1962 Redlinger 299/5 X 2,561,639 7/1951 Squires 299/4 3,050,290 8/1962Caldwell 299/5 X 2,969,226 l/196l Huntington 166/272 X 3,352,355 11/1967Putman 166/272 X 3,455,383 7/1969 Prats 166/254 3,322,194 5/1967Strubhar 166/271 X Primary Examiner-Robert L. Wolfe Attorney-George G.Pritzker and Harold L. Denkler [57] ABSTRACT A method of producinghydrocarbons and optionally water-soluble minerals from a subterraneanoil shale formation containing zone(s) of water-soluble minerals, bypenetrating said formation with at least one borehole and leaching ordissolving the water-soluble minerals from the formation with a solventfluid so as to form a cavern(s) and/or interconnected cavities, followedby fracturization and/or rubblization of the oil shale surrounding thecaverns or cavities, and thereafter injecting into fracturized and/orrubblized zones, a pyrolyzing fluid to effect in-situ hydrocarbonrecovery therefrom.

22 Claims, 20 Drawing Figures PAIENIEUSEPIBW 3.759.574

sum 01 or 11 FIG. 2 INVENTOR:

T. N. BEARD Pmmn-iusww 3759.574

saw 02 0F 11 I20 SOLUBILITY LBS/ BBL H20 00 TEMPERATURE, F

FIG. 3

FIG. 4

mvsmoa:

T. N. BEARD PATENTEDSEPI 8M8 3.759.574 m as nr 11 300 TEMPERATURE ATLEACHING FRONT INVENTOR: 6 T. N. BEARD BYzl/I K W Q/ 7 HIS AG NT SHALERESH WATER NAHCOLITE% SALT WATER SHALE FIG.5

FIG.

PATENTED 3.759.574

SHEET 05 0i 11 IOT- 50 ra ll 8 '5 c s a g HYDROCARBON GAS g s e j 30 6 gg E 3 I Q o w 0 I 4 o 20 o m w 8 2 v on.

O O l v l o 400 800 lzog/flsoo I TIME(DAYS) 30- FOOT RADIUS v OIL ANDHYDROCARBON GAS PRODUCTION RATES FOR nuaeuus RATE OF 0.02 FT/DAY.

FIG. 9

3: PRODUCED WATER 3- 5 I: I0 5 INJECTED STEAM 95% QUALITY v x I I I o400 800 I200 7 I600 TIME (DAYS) FOOT RADIUS INJECTED STEAM AND PRODUCEDWATER FOR RUBBLING RATE OF 0.02 FT/DAY FIG. IO

mag l HI AG N1" Pmamznserw m 3759.574

sum as or 11 PRODUCED NcIHCO X lO LB/DAY) r O 400 800 I200 I600T|ME(DAYS) 30'FOOT RADIUS PRODUCED NOHCO3 FOR RUBBLING RATE OF 0.02FT/DAY FIG. ll

INVENTOR:

T. N. BEARD PATENTEU SEP] 8 I973 WATER (TON DAY) OIL-STEAM RATIO (BBLIZXIO BTU ENTERING FORMATION) sum as or 11 PRODUCED WATER NJECTED STEAM95% QUALITY I 1 l 0 50 I00 I50 200 250 )3OO TIME (DAYS) 30-FO0T RADIUSINJECTED STEAM AND PRODUCED WATER FOR RUBBLING RATE OF 0.! FT/DAY FIG.l4

I l I50 200 TIME (DAYS) OIL-STEAM RATIO FOR RUBBLING RATE OF O.l FT/ DAYINVENTOR:

N. BEARD W 64 ms A ENT 1 FIG. l6

PAIENTEI] SEP] 8 I875 sum as or 11 m v w m I Qmi oi ooz z 082.0%

30 FOOT RADIUS TIME DAYS) PRODUCED N0HCO FOR RUBBLING RATE OF O.| FT/DAYFIG. l5

' PATENTEDSEPWQB SHEET 0F 11 2oo- 3 s: E 3 I50- 5 3 HYDROCARBON g 55 GASFIG. I7 52 50' a E ,1 Q g 5 3 on.

w g 50 I a: Q Q 3 8 O O I l l l I I 8 a 0 IO 20 4o 50 160 E 5 TIME(DAYS)30-FOOT RADIUS OIL AND HYDROCARBON GAS PRODUCTION RATES FOR RLBBLINGRATE OF 0.5 FT/DAY 200 PRODUCED WATER I50 3: S E INJECTED STEAM FIG. is8 00 95% QUALITY 05 U I 'E 0 I I I A 0 IO 20 3o 40 so RQ 5 TIME (DAYS)ao-FooT RADIUS g INJECTED STEAM AND PRODUCED WATER FOR RUBBLING RATECF05 FT/DAY 0.6- 5 2 5 Q4 '2 LI.) 2 a g E 02 A Q INVENTOR: P 0 I I I I II T. N. BEARD; g m 0 IO 20 30 40 /60 BY TIME (DAYS) so-FooT RADIUSOILSTEAM RATIO FOR RUBBLING RATE OF 0.5 FT/ DAY FIG. 20

IWI A L HIS AGENT PAIENIEU 3m 8 I873 SHEET 110F11 30" FOOT RADIUS TIME(DAYS) PRODUCED NQHCO FOR RUBBLING RATE OF 0.5 FT/ DAY FIG.

N BEARD METHOD OF PRODUCING HYDROCARBONS FROM AN OIL SHALE FORMATIONCROSS-REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of copending application Ser. No. 770,964, filedOct. 28, 1968 and now abandoned. Copending application Ser. No. 75,061and Ser. No. 75,067 filed Sept. 24, 1970 also are continuations -in-partof the application and claim subject matter similar to that claimedherein.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the recovery of hydrocarbons and optionally water-solubleminerals from underground oil shale formations containing water-solublemineral deposits. More particularly, it relates to hydrocarbon recoveryby in-situ thermal fluid extraction of oil shale within a fracturizedand/or rubblized portion of a subterranean oil shale formation in andaround a cavern and/or interconnected cavities formed by leaching ordissolving, e.g., solution mining of the watersoluble mineralstherefrom.

2. Description of the Prior Art Large deposits of oil in the form of oilshale are found in various sections of the United States, particularlyin Colorado and surrounding states and Canada. Various method ofrecovery of oil from these shale deposits have been proposed and theprincipal difliculty with these methods is their high cost which rendersthe recovered oil too expensive to compete with petroleum crudesrecovered by more conventional methods. Mining the oil shale andremoving the oil therefrom by above-ground retorting in furnacespresents a disposal and pollution problem and also such processes arealso generally commercially uneconomical. In-situ retorting to convertthe oil shale to recover the oil contained therein is made difficultbecause of the non-permeable nature of the oil shale. The art disclosesvarious means of improving oil recovery of oil from oil shale such asdescribed in US. Pat. Nos. 3,400,762 or 3,437,378, or 3,478,825 andparticularly various means of increasing permeability of oil shaleformations as described in US. Pat. Nos. 3,273,649 or 3,481,398 or3,502,372, or copending application Ser. No. 839,350, filed July 7,1969. Although these references are directed to an advancement of theart, the basic technique for recovering oil from oil shale stillrequires rubblization techniques such as by means of explosive devices,e.g., nuclear energy which is expensive, difficult to control andpresents a radioactive contamination problem, all of which are veryundesirable.

OBJECTS OF THE INVENTION It is an object of this invention to provide animproved method for recovering hydrocarbons from a water-soluble mineralcontaining oil shale formation by leaching or dissolving thewatersoluble minerals such as by solution mining so as to form a cavernand/or interconnected cavities within the oil shale formation.

It is a further object of the invention to effect rubblization and/orfracturization of the water-soluble mineral leached oil shale formationsurrounding the cavern and/or cavities so as to form a permeable zonethereby enhancing in-situ thermal fluid extraction (pyrolysis) ofhydrocarbons therefrom.

Still another object of this invention is to effect insitu pyrolysis toproduce hydrocarbons from oil shale subjected to leaching, rubblizationand/or fracturization as indicated in the previous two paragraphs, andsubsequently recovering the hydrocarbons by suitable means.

Still another object of the present invention is to recoverwater-soluble minerals from a rich water-soluble mineral containing oilshale formation(s) that may be removed during the leaching and/orsolution mining, rubblization and/or fracturization, and/or pyrolysisprocesses.

Still another object of the present invention is to sequentially and/orsimultaneously recover water-soluble minerals and hydrocarbons from richWater-soluble mineral containing oil shale formations that may beremoved during the leaching and/or solution mining, rubblization and/orfracturization and/or pyrolysis pro cesses.

Other objects of the invention will be apparent from the followingdescription.

SUMMARY OF THE INVENTION The present invention is directed to recoveryof hydrocarbons and optionally water-soluble minerals from water-solublemineral containing oil shale formations by the following steps: (1)subjecting a rich watersoluble mineral zone(s) of an oil shale formationto a leaching, dissolving or solution mining process so as to dissolveand preferably remove the water-soluble minerals, thereby creatingporosity to allow for thermal expansion of the oil shale and establishcommunication through the treated zone(s), (2) effecting in said leachedzone(s) rubblization and/or fracturization so as to form zone(s) ofrubblized and/or fractured oil shale with large surface area for moreefiicient heat treatment by in-situ thermal fluid extraction(pyrolysis), and (3) injecting into the rubblized and/or fracturized oilshale zone(s) a pyrolyzing fluid to effect hydrocarbon recovery.

The water-soluble mineral(s) and hydrocarbons may be recoveredsequentially or simultaneously and if the latter, the two products canbe separated by suitable means such as settling or solvent extractionabove ground. The oil shale formation may contain more than one zone ofrich water-soluble minerals which zones may be separated by impermeableoil shale layers of several feet to several hundred feet and each ofthese water-soluble mineral layers or zones can be leached or dissolvedor solution mined in accordance with the process of the presentinvention. Also, the water-soluble mineral zones may contain the same ordifferent minerals such as carbonates, bicarbonates, halites or mixturesthereof.

By water-soluble minerals present in the oil shale is meant to includewater-soluble silicates, halides, carbonates, and/or bicarbonates salts,such as alkali metal chloride, carbonate, bicarbonate and silicate,e.g., halite, trona, nahcolite and the like.

The first or initial step should be so designed to create a cavern orinterconnecting cavities in the watersoluble mineral bed(s) or zone(s)by dissolving, leaching or solution mining techniques through at leastone borehole penetrating said formation. Leaching can be efiected bycold or hot aqueous solutions either at atmospheric or elevatedpressures. When hot solutions are used such as hot water or acidifiedhot water and/or steam, more rapid dissolution is efl'ected of certainwater-soluble minerals such as nahcolite, trona, halite to produce voidspaces in the oil shale formation thereby providing and enhancing wellcommunication, space for thermal expansion of the shale, and greatersurface for contact with subsequent pyrolyzing fluid. Water can be coldor hot or steam or any other aqueous fluids can be used such as steamand/or water containing acids, e.g., HCl, or I-ICl I-IF, surfactants,sequestering agents, etc. If the initial cavities are not incommunication, fracturing may be necessary.

If necessary, fracturing the formation either before or after leachingby conventional means such as hydrofracturing, explosive means, nuclearmeans, etc., may be desirable. The leaching solutions can containchemical agents to enhance dissolution of the minerals. Under certainleaching conditions decomposition of certain water-soluble minerals,e.g., bicarbonates, into solublizing materials may take place of suchminerals as dawsonite and silicates which might be present in theformation, thereby increasing the porosity of the formation. Forexample, when nahcolite is dissolved with water, the pH of thedissolution fluid is increased and thereby aids in the dissolution ofsilicates, etc.

Leaching or solution mining of the water-soluble minerals such as haliteor nahcolite can be accomplished by a suitable solution mining techniquesuch as described in US. Pat. Nos. 2,618,475; 3,387,888; 3,393,013;3,402,966; 3,236,564; 3,510,167 or Canadian Pat. Nos. 832,828 or 832,276or as described in copending application Ser. No. 2,765 filed Jan. 17,1970. Spalling and rubbling can be accomplished by the method describedin US. Pat. No. 3,478,825 or by other means such as by hydraulic,explosive, nuclear and/or electrical means. Preferably rubblization isaccomplished by hot fluid circulation through the cavern causing thewalls to spall and fracture. In-situ thermal recovery of oil can beeffected by a pyrolyzing fluid such as steam and/or hot water or solventextraction means.

The circulation of a pyrolyzing fluid not only effects oil recovery butalso effects thermal rubbling and/or fracturization. Also, if thepyrolyzing fluid such as steam is used to extract and recover oil, moreminerals may be dissolved perpetuating the process.

By the term pyrolyzing fluid is meant a liquid or gas which by means ofthermal, chemical and/or solvent action, interacts with the kerogencomponents of an oil shale to produce and entrain hydrocarbon such assteam, Such a fluid can be hot fluids such as hot water of steam, ormixtures of hot water and strea, hot hydrocarbons and/or mixtures ofsuch fluids with chemicals such as acids, e.g., HCl and/or organicsolvents, benzene, toluene, cumene, phenol, etc. The kerogen pyrolyzingfluid can be heated by surface or borehole-located heating devices. Thekerogen-pyrolyzing fluid can advantageously comprise or contain asolvent for the soluble mineral, such as steam condensate or a hotaqueous solution of organic and/or inorganic acid, having a temperaturesuch as at least one hundred degrees Fahrenheit, such as from about 450F to above about l,500 F and preferably from about 550 F to l,000 F.Where the kerogen-pyrolyzing fluid contains or forms aqueous components,its circulation through the treated oil shale formation can enlarge thecavern, by solution mining the soluble minerals, while shale oil isbeing produced. Also, simultaneously or sequentially pyrolyzing and oilextracting fluids can be used such as steam followed by a solvent suchas phenol or benzene.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view,partly diagrammatic, of an embodiment of the invention showing aformation penetration by more than one well.

FIG. 2 is a sectional view of an embodiment of the invention, theformation being penetrated by a single well.

FIG. 3 is a graphical illustration showing the solubility of sodiumchloride (NaCl) and sodium bicarbonate (NaHCO in water as a function oftemperature.

FIG. 4 is a schematic illustration of a method for providingcommunication between a pair of well boreholes in accordance with thetechniques of this invention.

FIG. 5 is a schematic illustration partially in vertical sectionillustrating the mechanism of single-well salt leaching.

FIG. 6 is a graphical representation of maximum rate of nahcoliteleaching as a function of leaching fluid temperature.

FIG. 7 is a graphical representation of minimum time required to leach anahcolite cavity of lOO-foot radius as a function of leaching fluidtemperature.

FIG. 8 is a graphical representation showing estimated maximum time toleach a nahcolite cavity of l00-foot radius as a function of leachingfluid injection rate and temperature.

FIGS. 9-12 show graphical representations of various process parametersas a function of time in an example application of the process of thisinvention where the rubbling rate is 0.02 feet per day.

FIGS. 13-16 show graphical representations of various process parametersas a function of time in an example application of the process of thisinvention where the rubbling rate is 0.1 feet per day.

FIGS. 17-20 show graphical representations of various process parametersas a function of time for an example application of the process of thisinvention where the rubbling rate is 0.5 feet per day.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawing, a plurality of well boreholes are shown penetrating into asubterranean oil shale formation 9 which contain rich zones ofwatersoluble minerals 10, 10a and 10b. An injection well borehole 1 1 isshown extending into oil shale formation 9 and rich soluble mineralzone(s) 10 or multizones such as 10a and 10b that are located within theoil shale formation 9 and are also encountered by well borehole 12. Wellboreholes 11 and 12 are illustrated as having casings l3 and 14,respectively, cemented in place in their respective boreholes bysuitable sealants 15 through 16, respectively. Although only a singleinjection well borehole 11 and a single production well borehole 12 havebeen illustrated, obviously various combinations of one or moreinjection and production wells may be provided by one skilled in theart.

In carrying out the method of this invention, the location of zones richin substantially water-soluble minerals is determined in a conventionalmanner.

Fluid communication between well boreholes l1 and 12 (FIG. 1) and thezones rich in water-soluble minerals therebetween may be established bysolution mining a cavern or cavities 23, through the soluble mineralzones. Communication can be enhanced by means of conventional hydraulic,electric, and/or explosive fracturing techniques, all well known in theart. Where, for example, subterranean stresses in and around solublemineral zones 10, a and 10b are conducive to the formation of horizontalfractures, the fluid communication between well boreholes 11 and 12 andthe soluble mineral can be established by a conventional hydraulicfracturing technique. Referring to FIG. 1, after fluid communication hasbeen established between a pair of wells, aqueous leaching or solutionmining liquid is injected through tubing 17 down well borehole 11, outthrough perforations 18 opposite any or all of the soluble beds throughthe bed 10, 10a and/or 10b up borehole 12 through tubing via perforationl9 creating a leached cavern 23. The aqueous liquid may comprise waterand/or steam or aqueous solutions of acid or acid-forming materials andis circulated at pressures either above or below the over-burdenpressure. The circulating aqueous liquid dissolves the water-solubleminerals and mineral byproducts thereof are recovered from the fluidflowing out of well borehole 12, for example, by conventionalevaporation and/or precipitation procedures.

Fluid communication can also be established in one borehole between atleast two spaced portions of the well borehole and the water-solubleminerals (as for example, in FIG. 2 communication is through the tubingstring the ends of which are open to the water-soluble minerals and somedistance apart.) Thus a single well may be utilized by a dual zonecompletion arrangement as shown in FIG. 2 such that fluids can beinjected at one point of the well and produced from another point of thesame well. In FIG. 2, the wellbore is 26, the easing is 27, the sealantis 28, within the casing are the injection tubing string 29 andproduction tubing string 30, the borehole 26 penetrates oil shaleformation 9 with mineral zone(s) 10 or or multizones 10a and 10b.

Fracturing pressures are generated within the oil shale formation 9while lower pressures are maintained within the cavern 23 which isformed within oil shale formation-9 by the removal of the water-solubleminerals. These pressures are preferably generated by merely circulatinghot fluid through cavern 23. As the walls of the cavern(s) 23 (23a FIG.2) are heated kerogen is pyrolyzed within the cavern walls and thepressures of the pyrolysis products increase until portions of the wallsare spalled into the cavern 23 creating a rubblized zone 24 (24a FIG. 2)and surrounding fracture area 25 (25a FIG. 2).

Alternatively, fracturization and/or rubblization can be accomplished byconventional means such as hydraulic, explosive means and the like. Toprovide additional void space, if necessary, further leaching can beconducted.

Finally, a kerogen-pyrolyzing fluid such as steam is circulated fromwell borehole 11 (FIG. 1) through the rubblized zone 24 and fracturedzone 25 of oil shale formation 9 and out of well borehole 12.Hydrocarbon materials are then recovered from the heated fluidcirculatingout of well borehole 12 by means well known in the art.Removal of hydrocarbons fromthe oil shale provides additional void spaceenlarging the original rubblized zone, perpetrating the process. Similartechniques can be applied to single wells as shown in FIG. 2.

Conventional equipment and techniques, such as heating means, pumpingmeans, separators and heat exchangers may be used for pressurizing,heating, injecting, producing and separating components of the heatedfluid circulating through the oil shale formation 9. The production ofthe fluid may be aided by downhole pumping means, not shown, orrestricted to the extent necessary to maintain the selected pressurewithin the oil shale formation 9.

The fluid circulated through rubblized zone 24 and fractured zone 25(FIG. 1) to recover oil shale from oil shale formation 9 may compriseany heated gas, liquid or steam. Oil shale reactive properties may alsobe imparted to the circulating fluid as discussed hereinabove.

Where the oil formation contains a zone rich in substantiallywater-soluble minerals in which zone the soluble minerals occur in theform of adjacent but discrete nodules or lenses 31, or the like, thepresent process is applied as described above. In this situation, thecaverns comprise a network of relatively small cavities that areinterconnected by fractures.

EXAMPLES Leaching Phase A. In a continuous oil shale formationcontaining a nahcolite bed, a pair of wells are completed into anahocolite layer at 2,100 feet with a downhole well separation of feet.Solution mining of the nahcolite (NaHCQ by injection of hot watertherein provides both communication between the wells and the void spacenecessary to effect fragmentation and subsequent in-situ thermaltreatment of the formation to recover oil.

In such a situation a bulk density (p) was found to be a 2.2 gin/cc andthe permeability (K) was found to be 0.065 millidarcy for the nahcolitelayerat about 2,055 feet. Experimentally, samples of this nahcolite werefound to be completely dissolved in hot water, leaving 6 percent byweight insolubles.

Minimum volumes of water required to establish a channel 1 foot wide,three feet high and 70 feet long (between two wells about 50 feet apart,for example) which contains 13.4 tons of nahcolite may be determinedfrom the solubility of sodium carbonate and bicarbonate in water.

As can be seen in FIG. 3 the solubility of pure Nal-ICO in water atformation temperature F) is about 30 lbs/bbl. Thus, a minimum of 700bbls of water is required to establish communication between wells. Onthe other hand, a cylindrical cavity of the same height but 50 feet inradius contains 1,620 tons of nahcolite, and requires at least 10" bblsof water at formation temperature.

Water requirements may be reduced by a factor of five if the water isheated to 400 F (AT 310 F). Heating the water also has the addedadvantage that it results in a higher dissolution rate. Thus heating thewater results in a shorter operating life, and requires the handling ofrelative small volumes of water. On the other hand, it requires the useof heaters with their attendant requirements of water quality and fuelsupply. Also, the water disposal lines may become plugged withprecipitate as the temperature of the line drops at the surface.

If the water is injected at formation temperature, a slight reduction intemperature takes place. The heat of solution of sodium bicarbonate is 4kcal/mole, which results in as much as a 10 F drop in the solutiontemperature. Because the solution is not saturated, the observedtemperature drops are in fact much smaller and thus may be discounted.

The addition of acids, such as 15 percent HCl to mining solutions isbeneficial since it generally may be expected to result in a reductionin operating time, because of the high rate of reaction between the acid(HCl) and nahcolite. For example, injection of an acid solution into thewellbore will speed up the rate at which the cavity is made.

Communication may be established between the two wells by means ofmechanical nozzles having controllable orientation through which thesolvent is introduced. As illustrated schematically in FIG. 4, where theuncertainty in orientation of the nozzles is 1: 10, the nozzles may bedirected from both wells A and B, with the orientation of the nozzlesranging from to 15 from their centerlines. This procedure insureseventual communication between the wells and reduces the time to obtaincommunication.

The degree of saturation of the effluent liquid is closely related tothe mean residence time of the fluid in the subsurface, the circulationpattern of the fluid, and the rate at which the nahcolite goes insolution. The solution efficiency may be increased by increasing theresidence time, that is, by increasing the operating time. Wheresufficient water capacity is available and the operating time is to bekept low, it would appear that low solution efficiencies may betolerated, especially if it is not intended to heat the water. On theother hand, the mining effect may be greatly enhanced if fragmentsresulting from jetting are removed as so]- ids.

After solution mining to form the cavern, the formation is fractured inthe vicinity of the cavern and oil is recovered therefrom by means ofin-situ oil recovery means as is well known in the art.

B. Results for a single well leaching to a l00-foot radius wasdetermined experimentally for a nahcolite layer oil shale. The leachingrate results show that leaching rates are a function of temperature.

FIG. 5 shows the mechanism of single well salt leaching. Fresh waterenters at the top of the formation and flows along the top of thecavity. Once it reaches the salt layer it dissolves the salt, becomingdenser. The denser fluid then flows to the bottom of the cavity alongthe edge of the salt. There are two important parameters which controlthe rate of frontal advance of the cavity, natural convection anddiffusion in the vertical direction. The slowing of the frontal advanceis caused by diffusion in the vertical direction from the salt solutionto the incoming fresh water. As the concentration of salt in the waterreaching the leading edge of the cavity increases, the rate of frontaladvance slows proportionally.

An experiment was scaled for 2,000 bpd at room temperature in a 6-footlayer of NaCl. This corresponds to scaling nahcolite leaching in thesame size layer at 8,300 bpd and 300 F. It was found that the rate offrontal advance was constant out to the scaled test radius of 100 feet.The concentration of salt in the produced solution increased from 12percent of saturation to 85 percent of saturation during the course ofthe experiment.

Using the results of the experiment, estimates were made of the maximumleaching rate of the subject nahcolite layer as a function of thetemperature of the fluid at the leading edge of the cavity. Since aperfectly circular pattern was not obtained in the experiment, theminimum leaching rate was used in the estimates. It was also assumedthat there were 20 percent insolubles in the nahcolite and that theironly effect was in reducing the available surface area for leaching.FIG. 6 shows the rate of leaching as a function of the temperature ofthe fluid at the leading edge. FIG. 7 shows the minimum time required toleach a IOO-foot radius as a function of temperature. It appears that aflow rate of 2,000 bpd should be practical for a 6-foot layer.

The test showed that the production well was producing saturatedsolution when the frontal advance rate decreased and the maximum timerequired to leach a l00-foot radius can be calculated from a materialbalance and the solubility of nahcolite in water. FIG. 7 shows thisminimum leaching time as a function of leaching time and flow rate. Inmaking the calculations for FIG. 7, the constraint that the rate ofadvance could not exceed the maximum values given in FIG. 6 was used.

FIG. 8 shows the effect of temperature on water injection rates leachinga cavity with a radius of feet.

It should be noted that the temperature at the leading edge of theadvancing front will not be the same as the injected temperature due toheat losses to the shale. The temperature drop will be roughlyproportional to the temperature difference between the injected fluidand the initial shale temperature and will increase as the frontadvances.

Rubblization Phase Following the leaching phase rubbling using hot waterand steam on the oil shale was performed. This consisted of cementing alarge rectangular block of oil shale into a stainless steel containersuch that the lower 3 k inches of the block was unconfined and wascontacted with hot water or steam. A spring-loaded plate positionedbelow the block allowed for the detection of any falls occurring duringthe experiment. Thermocouples placed in the steam chamber and into theshale block monitored the temperature at these points. Pressuressurrounding the shale were maintained at 900 to 1,000 psi with nitrogengas.

Three tests (A B, and C,) were run under essentially the sameconditions. The first, A utilized a lean shale block (8 gal/ton); thelower face of the block was contacted with 500 F steam for a 6-dayperiod. At the conclusion of the test, the shale container was openedand the block examined, and it was only evidented that the steam inducedconsiderable cracking and rubbling. No oil was recovered during or afterthe experiment.

The second test, 8,, was essentially a repeat of A using a richer shale(27 gal/ton) and a different heating medium, hot water instead of steam.The water temperature was held constant for a lor 2-day period and thenraised in 50 F increments. The water temperature was raised and heldconstant at 300 F for 16 hours. Several large cracks inch to A inchwide) were developed even at these mild temperatures. After a daysdelay, the test was restarted and a major fall occurred (watertemperature 350 F). Smaller falls of 5 to 10 pounds occurred at 25hours. The test was terminated after 312 hours; the maximum temperature,520 F, maintained for the last 51 hours. No oil was detected in theeffluent water stream, but the outlet lines were 9 found to be coatedwith a tarry residue readily soluble in benzene.

The results of I3 indicated that rubbling took place even at mildtemperatures (350 F).

Test C, was run under conditions similar to B, and the specificconditions are shown in Table 1.

Table 1 C TEST CONDITIONS Water Temp. Time at Temp. Shale Temp. Pressure(F) (hours) (F) (psi) temperature was then reduced in 50 increments.Total test time 312 hours (13 days) crystalline material.

Heating the shale four days at 520 F resulted in greatly increasedfracturing over that resulting from heating'to 450 F. After heating at450 F, many cracks had formed, but none completely cleaved the slab.After heating to 520 F, a number of these cracks had been considerablywidened and had propogated through the entire extent of the slab. Thestrain, measured for the slab, had increased to 0.057 and average slabthickness increased from 4 to 4- inches. No oil was produced with theeffluent water.

Peculiar to test C, was the correlation between the positions of beddingplane distortions and the occurrence of vertical cracks upon heating.The previous sample B, was very evenly bedded and did not show thisbehavior.

In summary, the amount of fragmenting and fracturing of oil shaleincreased with increasing richness of the oil shale sample. There was asignificant increase in fracturing at T 520 F over that produced below450 F in unconfined shale samples. Good correlation exists between thepositions of vertical (perpendicular to the bedding) cracks and thepositions of distortions in the bedding plane.

Recovery Phase Calculations were made to estimate the performance ofashale oil recovery project in accordance with the method of thisinvention wherein steam is used as the pyrolyzing fluid to effecthydrocarbon recovery as well as recovery of other products as shown inFIGS. 9-20.

The basic data used for thecalculations were: a. steam injection at 625F, 95 percent quality, b. 10 tons of steam condensed coming downinjection .pipe,

- are for a rubbling rate of 0.02 ft/day, FIGS. 13-16 are for a rubblingrate of 0.1 ft/day, and FIGS. 17-20 are for a rubbling rate of 0.5ft/day.

It is understood that various changes in the detailed described toexplain the invention can be made by persons skilled in the art withinthe scope of the invention as expressed in the appended claims. I claimas my invention:

1. A method of producing hydrocarbons from a subterranean oil shaleformation containing zones of water-soluble minerals comprising thesteps of:

a. extending at least one well borehole into the watersoluble mineralcontaining zone of the oil shale formation;

b. removing water-soluble minerals by leaching, dissolving or solutionmining with a non-acidic fluid, thereby creating porosity in said zoneof the formation;

c. effecting rubblization' and fracturization of oil shale adjacentleached zone (b);

d. injecting'into said rubblized, fracturized oil shale a pyrolyzingfluid; and

e. recovering hydrocarbons from said rubblized fracturized oil shale.

2. The method of claim 1 wherein the leaching solution (b) is hot water,and the pyrolyzing fluid is steam.

3. A method of producing oil from a subterranean oil shale formationcontaining a zone of water-soluble minerals comprising the steps of:

creating a cavity in the oil shale formation by circulating aqueous anon-acidic solution-mining fluid into the water-soluble mineral zonethrough a first well, and out of the water-soluble mineral zone througha second well;

recovering the water-soluble mineral from aqueous fluid circulating outof the second well;

fracturing and rubbling the oil shale formation surrounding the cavity;

flowing a kerogen-pyrolyzing fluid into the fractured and rubblizedformation; and

recovering oil from the pyrolyzed treated fracturized and rubblizedformation. 4. A method for producing oil from a subterranean oil shaleformation having at least one zone which contains water soluble mineralscomprising the steps of:

extending at least one well borehole into said formation and into saidzone;

establishing fluid communication between said well borehole and saidzone at at least two spaced locations within said well;

circulating aqueous liquid from one of said spaced locations to anotherin contact with said zone to dissolve water-soluble minerals and leave afluid filled cavern within the oil shale formation while maintainingfluid pressures within said cavern below overburden pressure withinother regions in said oil shale formation;

generating fluid pressures within said oil shale formation sufiicient tocreate fractures and displace solid oil shale material toward and intosaid cavern;

flowing a kerogen-pyrolyzing fluid from one of said locations to anotherthrough the fractures and cavern within the oil shale formation;

outflowing kerogen-pyrolyzing fluid from said well;

and

recovering shale oil from outflowing portions of said kerogen-pyrolyzingfluid.

5. A method for producing oil from a subterranean oil shale formationhaving at least one zone which contains water soluble minerals,comprising the steps of:

extending at least one well borehole into said formation and into saidzone;

establishing fluid communication between at least one well borehole andsaid zone at at least two spaced locations within said well; circulatingaqueous liquid from one of said spaced locations to another in contactwith said zone to dissolve water-soluble minerals and leave afluidfilled cavern within the oil shale formation while generating fluidpressure within said oil shale formation sufficient to create fracturesand displace solid oil shale material toward and into said cavern;

flowing a kerogen-pyrolyzing fluid from one of said locations, toanother through the fractures and cavern within the oil shale formation;

outflowing kerogen-pyrolyzing fluid from said well;

and

recovering shale oil from outflowing portions of said kerogen-pyrolyzingfluid.

6. The method of claim including the step of establishing fluidcommunication between said borehole locations through said zonewater-soluble mineral by hydraulically fracturing at least a portion ofsaid oil shale formation containing said zone.

7. A method of claim 5 including the step of establishing fluidcommunication between said borehole locations through said zonewater-soluble mineral by explosively fracturing at least a portion ofsaid oil shale formation containing said zone.

8. The method of claim 5 including the step of establishing fluidcommunication between said borehole locations through said zonewater-soluble mineral by electrically fracturing at least the portion ofsaid oil shale formation communicating with said well boreholes.

9. The method of claim 5 wherein the step of circulating aqueous fluidincludes the step of imparting acidic properties to said aqueous fluidand circulating said fluid liquid at pressures above the overburdenpressure.

10. The method of claim 5 wherein the step of circulating aqueous liquidincludes the step of imparting acidic properties to said aqueous fluidand ciculating said aqueous fluid at pressures below the overburdenpressure.

11. The method of claim 5 wherein the step of generating fluid pressuressufficient to create fractures is carried out by the step of circulatingfluid through said cavern at a temperature sufficient to pyrolyze thekerogen within the oil shale adjacent to the walls fonning said cavernand to spall-off portions of said walls into said cavern.

12. The method of claim 5 wherein the step of generating fluid pressuressufficient to create fractures is carried out by the step of pumpingfluid explosives into said cavern; and

detonating said explosives so as to produce an initial pulse of highpressure within the cavern followed by a pressure that becomes lowerthan that within the adjacent oil shale formation thereby displacingsaid solid material towards said cavern.

13. The method of claim 1 including the step of establishing fluidcommunication between at least a pair of well boreholes within saidmineral containing zone, said communication being accomplished byjetting aqueous liquid from each of said well boreholes to a pointintermediate said boreholes.

14. A method of producing oil from a subterranean oil shale formationcontaining rich water-soluble mineral zones comprising the steps of:

a. subjecting the formation to leaching of the watersoluble minerals byinjecting into the formation a non-acidic leaching solution to leach outthe minerals and thereby effecting a zone of communicating cavities inthe formation;

b. injecting a kerogen-pyrolyzing fluid into cavities zone (a) of theformation so as to effect spalling and rubblization of the oil shale;

c. continuing injection of the kerogen-pyrolyzing fluid to effect oilextraction; and

d. recovering the oil.

15. The method of claim 14 wherein the solvent is an aqueous liquid andthe kerogen-pyrolyzing fluid is steam.

16. The method of claim 14 wherein the watersoluble mineral iswater-soluble carbonate, the watersoluble leaching solution is hot waterand the kerogenpyrolyzing fluid is steam.

17. The method of claim 15 wherein the watersoluble mineral isnahcolite.

18. The method of claim 5 wherein the water-soluble minerals arerecovered from the formation prior to injection of thekerogen-pyrolyzing fluid.

19. The method of claim 3 wherein the dissolved water-soluble mineralby-products are recovered prior to flowing kerogen-pyrolyzing fluid intothe formation.

20. The method of claim 5 wherein the aqueous liquid is hot water andthe kerogen-pyrolyzing fluid is steam.

21. The method of claim 20 wherein the watersoluble mineral iswater-soluble carbonate.

soluble mineral is nahcolite.

2. The method of claim 1 wherein the leaching solution (b) is hot water,and the pyrolyzing fluid is steam.
 3. A method of producing oil from asubterranean oil shale formation containing a zone of water-solubleminerals comprising the steps of: creating a cavity in the oil shaleformation by circulating aqueous a non-acidic solution-mining fluid intothe water-soluble mineral zone through a first well, and out of thewater-soluble mineral zone through a second well; recovering thewater-soluble mineral from aqueous fluid circulating out of the secondwell; fracturing and rubbling the oil shale formation surrounding thecavity; flowing a kerogen-pyrolyzing fluid into the fractured andrubblized formation; and recovering oil from the pyrolyzed treatedfracturized and rubblized formation.
 4. A method for producing oil froma subterranean oil shale formation having at least one zone whichcontains water soluble minerals comprising the steps of: extending atleast one well borehole into said formation and into said zone;establishing fluid communication between said well borehole and saidzone at at least two spaced locations within said well; circulatingaqueous liquid from one of said spaced locations to another in contactwith said zone to dissolve water-soluble minerals and leave afluid-filled cavern within the oil shale formation while maintainingfluid pressures within said cavern below overburden pressure withinother regions in said oil shale formation; generating fluid pressureswithin said oil shale formation sufficient to create fractures anddisplace solid oil shale material toward and into said cavern; flowing akerogen-pyrolyzing fluid from one of said locations to another throughthe fractures and cavern within the oil shale formation; outflowingkerogen-pyrolyzing fluid from said well; and recovering shale oil fromoutflowing portions of said kerogen-pyrolyzing fluid.
 5. A method forproducing oil from a subterranean oil shale formation having at leastone zone which contains water soluble minerals, comprising the steps of:extending at least one well borehole into said formation and into saidzone; establishing fluid communication between at least one wellborehole and said zone at at least two spaced locations within saidwell; circulating aqueous liquid from one of said spaced locations toanother in contact with said zone to dissolve water-soluble minerals andleave a fluid-filled cavern within the oil shale formation whilegenerating fluid pressure within said oil shale formation sufficient tocreate fractures and displace solid oil shale material toward and intosaid cavern; flowing a kerogen-pyrolyzing fluid from one of saidlocations, to another through the fractures and cavern within the oilshale formation; outflowing kerogen-pyrolyzing fluid from said well; andrecovering shale oil from outflowing portions of said kerogen-pyrolyzingfluid.
 6. The method of claim 5 including the step of establishing fluidcommunication between said borehole locations through said zonewater-soluble mineral by hydraulically fracturing at least a portion ofsaid oil shale formation containing said zone.
 7. A method of claim 5including the step of establishing fluid communication between saidborehole locations through said zone water-soluble mineral byexplosively fracturing at least a portion of said oil shale formationcontaining said zone.
 8. The method of claim 5 including the step ofestablishing fluid communication between said borehole locations throughsaid zone water-soluble mineral by electrically fracturing at least theportion of said oil shale formation communicating with said wellboreholes.
 9. The method of claim 5 wherein the step of circulatingaqueous fluid includes the step of imparting acidic properties to saidaqueous fluid and circulating said fluid liquid at pressures above theoverburden pressure.
 10. The method of claim 5 wherein the step ofcirculating aqueous liquid includes the step of imparting acidicproperties to said aqueous fluid and ciculating said aqueous fluid atpressures below the overburden pressure.
 11. The method of claim 5wherein the step of generating fluid pressures sufficient to createfractures is carried out by the step of circulating fluid through saidcavern at a temperature sufficient to pyrolyze the kerogen within theoil shale adjacent to the walls forming said cavern and to spall-offportions of said walls into said cavern.
 12. The method of claim 5wherein the step of generating fluid pressures sufficient to createfractures is carried out by the step of pumping fluid explosives intosaid cavern; and detonating said explosives so as to produce an initialpulse of high pressure within the cavern followed by a pressure thatbecomes lower than that within the adjacent oil shale formation therebydisplacing said solid material towards said cavern.
 13. The method ofclaim 1 including the step of establishing fluid communication betweenat least a pair of well boreholes within said mineral containing zone,said communication being accomplished by jetting aqueous liquid fromeach of said well boreholes to a point intermediate said boreholes. 14.A method of producing oil from a subterranean oil shale formationcontaining rich water-soluble mineral zones comprising the steps of: a.subjecting the formation to leaching of the water-soluble minerals byinjecting into the formation a non-acidic leaching solution to leach outthe minerals and thereby effecting a zone of communicating cavities inthe formation; b. injecting a kerogen-pyrolyzing fluid into cavitieszone (a) of the formation so as to effect spalling and rubblization ofthe oil shale; c. continuing injection of the kerogen-pyrolyzing fluidto effect oil extraction; and d. recovering the oil.
 15. The method ofclaim 14 wherein the solvent is an aqueous liquid and thekerogen-pyrolyzing fluid is steam.
 16. The method of claim 14 whereinthe water-soluble mineral is water-soluble carbonate, the water-solubleleaching solution is hot water and the kerogen-pyrolyzing fluid issteAm.
 17. The method of claim 15 wherein the water-soluble mineral isnahcolite.
 18. The method of claim 5 wherein the water-soluble mineralsare recovered from the formation prior to injection of thekerogen-pyrolyzing fluid.
 19. The method of claim 3 wherein thedissolved water-soluble mineral by-products are recovered prior toflowing kerogen-pyrolyzing fluid into the formation.
 20. The method ofclaim 5 wherein the aqueous liquid is hot water and thekerogen-pyrolyzing fluid is steam.
 21. The method of claim 20 whereinthe water-soluble mineral is water-soluble carbonate.
 22. The method ofclaim 20 wherein the water-soluble mineral is nahcolite.